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                [SHOI2014]信号增幅仪                 </h1>
                <p>时间限制：40s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div>无线网络基站在理想状况下有效信号覆盖范围是个圆形。而无线基站的功耗与圆的半径的平方成正比。现给出平面</div>
<div>上若干网络用户的位置,请你选择一个合适的位置建设无线基站....就在你拿起键盘准备开始敲代码的时候,你的好</div>
<div>朋友发明家 SHTSC 突然出现了。SHTSC 刚刚完成了他的新发明&mdash;&mdash;无线信号增幅仪。增幅仪能够在不增加无线基</div>
<div>站功耗的前提下,使得有效信号的覆盖范围在某一特定方向上伸长若干倍。即:使用了增幅仪的无线基站覆盖范围是</div>
<div>个椭圆,其功耗正比于半短轴长的平方。现给出平面上若干网络用户的位置,请你选择一个合适的位置建设无线基站</div>
<div>,并在增幅仪的帮助下使所有的用户都能接收到信号,且无线基站的功耗最小。注意:由于SHTSC 增幅仪的工作原理</div>
<div>依赖地磁场,增幅的方向是恒定的。</div></p><hr/><h3>输入格式</h3><p><div>第一行一个整数:n。平面内的用户个数。之后的 n 行每行两个整数 x, y,表示一个用户的位置。第 n+2 行一个整</div>
<div>数:a。表示增幅仪的增幅方向,单位是度。表示增幅仪的方向是从 x 正方向逆时针转 a 度。第 n+3 行一个整数:p</div>
<div>。表示增幅仪的放大倍数。</div></p><hr/><h3>输出格式</h3><p><p>输出一行一个实数,为能够覆盖所有用户的最小椭圆的半短轴长,四舍五入到三位小数。</p></p><hr/><h3>样例输入</h3><pre>样例一：
2
1 0 
-1 0 
0 
2 </pre><hr/><h3>样例输出</h3><pre>样例一：
0.500</pre><hr/><h3>提示</h3><p><p><span style="font-size: medium">对于 100%的数据,n&le;50000,0&le;a&lt;180,1&le;p&le;100,|x|,|y|&le;2&times;10^8。</span></p></p><hr/><h3>题目来源</h3><p>By 佚名提供</p>
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